whpx: Fixed incorrect CR8/TPR synchronization

This fixes the following error triggered when stopping and resuming a 64-bit
Linux kernel via gdb:

qemu-system-x86_64.exe: WHPX: Failed to set virtual processor context, hr=c0350005

The previous logic for synchronizing the values did not take into account
that the lower 4 bits of the CR8 register, containing the priority level,
mapped to bits 7:4 of the APIC.TPR register (see section 10.8.6.1 of
Volume 3 of Intel 64 and IA-32 Architectures Software Developer's Manual).
The caused WHvSetVirtualProcessorRegisters() to fail with an error,
effectively preventing GDB from changing the guest context.

Signed-off-by: Ivan Shcherbakov <ivan@sysprogs.com>
Message-Id: <010b01d82874$bb4ef160$31ecd420$@sysprogs.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>